The specific aim of this study is to develop and test new classes of contrast agents to facilitate microscopic MRI mapping of organisms. The agents will permit the long term analysis of cell movements and axonal projects in developing and adult brains of experimental animals. The approach will involve the synthesis of stable chelating agents have been chemically modified so they can be attached to a variety of biomolecules. The design and synthesis of new contrast agents is divided into two parts: 1) the synthesis of a series of stable and chemically versatile complexes that are effective MR contrast agents and 2) selective attachment of these complexes to physiologically interesting moieties. A long term goal of this proposal is the design and development of a new classes of MRI contrast agents that are capable of reporting on in-vivo anatomical and physiological properties of living organisms. The ability to differentiate regions or tissues that may be magnetically similar but histologically distinct is a major impetus for the preparation of these agents. Current MRI agents are limited in their ability to target specific anatomical regions or cellular targets in clinical or experimental settings and no MR agents are capable of reporting on gene expression in the form of an MR image.